Points of rock hung from the ceiling, piercing the water’s surface and extending down another few feet like upside down porcupine spines. Ripples surrounded them and, with our lights, they seem to float detached, in mid-air. Or really, in water.

Yeah, this was definitely a trip to another planet. Or closer, Carlsbad Caverns without the gravity. We were flying, weightless, in it all.

Scuba diving in a cenote, or water- filled cavern, in Mexico is like nothing else you’ve ever seen.

And Akumal, midway down Mexico’s Riviera Maya on the Yucatan Peninsula, is the only place on earth you can do this without a ton of training.

You need only open ocean scuba certification for two reasons: You stay in the “cavern zone,” meaning you can always see at least a glow of outside light. Plus, there are these really competent cave trained guides to lead you and, if necessary, hold your hand.

What caused all these incredible formations is limestone and rainwater. Rain turns a bit acid on limestone and slooowly eats the rock away. Thousands of years later, you have dry tunnels. But the water still drips and then causes stalactites, stalacmites, flowstones and lots more. Then some of these caves fill back up with water and, voila, you’ve got a weightless landscape like no other.

Early Mayas (there are, by the way, still real Mayas around, and they’re called Mayas, not Mayans) believed that these cenotes were the entrance to Xibalba — the feared underground. They were sacred places of worship and, legends say, sacrifice. They were also the only source of fresh water, which made them even more precious.

There are hundreds of such diveable caves and caverns here, though the ones limited to cavern divers top out at about a dozen.

First my fellow divers and I did Dos Ojos (or, two eyes — named thusly for its two entrances). This is the novice cave. Large, open, easy to swim. But one of our divers was a bit uneasy about all that dark. She grabbed our guide’s hand and they stayed connected for the rest of the dive.

Inside the tunnels, it looks like the world had melted and dribbled onto the cave walls. This is flowstone — minerals paint the rock in orange, beige, white and black like some crazy modern art.

Beyond, the guide pointed upward, signaling us to surface in an air- filled chamber called the Bat Cave. Sure enough, the furry little critters winged their way around the room, letting out an occasional high-pitched squeal. But mostly, they hung upside down in holes in the ceiling, twitching their cute little noses.

Farther on, the tunnel curved gently, all the while lined in curtains of folded rock, sometimes smooth, sometimes sharp. Mirror bubbles of exhaled air flattened themselves across the ceiling in yard-wide silver plates. And back at the entrance, hundreds of tiny fish surrounded us in clouds and tickled our faces.

In another cavern, the entrance was silhouetted with branches, roots and rocks. Above the hole, a tangle of tropical trees rose into the sky.

And because the water is fresh, not salt, it’s clear as air. You could count the fronds on the palm trees from 25 feet down.

Small fish flitted about, glittering like silver foil in the sunlight. And the rays of light were spectacular. The beams were broken into waving curtains that turned the entire scene into something unreal.

But wow, that was just the introduction. Of the five dives I did, by far the best was Dream Gate.

Going into this place is like swimming down the throat of Jaws. We swam through jagged points coming from the ceiling and the floor. And immediately, we were surrounded by points of rock hanging from the ceiling in sprays of sharp spines. They continued on like this for the entire hour-long dive … folded walls and fragile columns so thin, you could have circled them with your fingers. Sometimes, the columns were smooth, with colors dripping vertically but more often, they had horizontal rings, like a million paper-thin plates stacked atop each other.

We saw shrimp and catfish and always, those tiny fish called tetras.

And when we came out, gliding through the columns and spires, it was as if we had been spit out of some gigantic creature’s mouth. Into Jaws and out again.

HOW TO GO

The spring-fed water in the cenotes runs about 77 degrees, so a shorty wetsuit is recommended, and because you are in fresh water, you can eliminate half the weight you would use in the ocean.

For cavern diving, you need only standard open water scuba gear, along with two battery powered lights but no snorkel. You stay within sight of natural daylight. Non-cave certified divers can dive cenotes only with a guide. A sample price is $70 US for one tank, $130 US for two. Decent quality rental gear is also available.

Gear up for your adventure by contacting the Akumal Dive Center, a reliable local outfitter. They’re at akumaldivecenter.com.